In general, in order to improve fuel efficiency of an engine that uses hydrocarbon fuel, technical improvement about an engine, an accessory device, friction, and the like is mainly performed at a power generation step through weight reduction, a turbocharger, a fuel injection system, a cooling system, and down-sizing.
However, in recent years, researches and developments are actively conducted on a technology that recovers waste energy, which is wasted through emission gas, an engine coolant, and the like, and converts the waste energy into electrical energy or mechanical energy after the power generation step.
The main reason why interests are focused on the technology of recovering waste energy is that an amount of energy wasted from an engine is still considerable even though the engine has high efficiency, and it is determined that technical developments on combustion devices and engine peripheral devices for improving fuel efficiency have somewhat reached the limit.
That is, the reason is that referring to energy balance of a diesel engine for a large-scale and commercial truck as an example of an engine having improved efficiency, maximum energy conversion efficiency of fuel is merely 42%, remaining 31% is wasted in the form of mechanical friction and cooling loss, and remaining 27% is wasted in the form of exhaust energy, and as a result, the technology still cannot overcome the limit.
Accordingly, as technologies of improving fuel efficiency utilizing waste energy, which are most actively researched at present, there are the turbo compound technology which recovers kinetic energy of engine emission gas, and the thermo-electric generator technology and the Rankine steam cycle technology which recover thermal energy from emission gas, engine coolant, and the like.
Among the technologies, only the turbo compound technology is actually applied to several medium-scale or large-scale trucks, and a turbo compound system has a blow-down turbine, which is further mounted in an engine exhaust system in addition to a turbocharger turbine used for intake air supercharging of fuel air, so as to recover waste energy of emission gas, and is classified into a mechanical type and an electric type in accordance with a manner of transferring energy recovered from the blow-down turbine.
As illustrated in FIG. 1, the mechanical type supplies compressed air for fuel to an engine 10 by operating a turbocharger compressor 12 using a turbocharger turbine 11, which converts emission gas energy of the engine 10 into mechanical work, and particularly, transfers power produced by the blow-down turbine 20 to a crank shaft 40 through a mechanical power transmission device 30a including a transmission 31a and a speed-reducing gear 32a, thereby increasing output of the engine 10 without additional fuel consumption.
As illustrated in FIG. 2, the electric type supplies compressed air to the engine 10 by operating the turbocharger compressor 12 using the turbocharger turbine 11, and particularly, transfers power produced by the blow-down turbine 20 to the crank shaft 40 through an electric power transmission device 30b including a generator 31b, and a motor 32b, thereby converting emission gas energy into electrical energy, and utilizing the electrical energy.
Meanwhile, the related art recycles waste energy of emission gas of the engine 10, as described above, so as to increase output of the crank shaft 40, and as illustrated in FIG. 3, compresses a refrigerant by connecting a compressor of an air conditioner 50 for a vehicle and the crank shaft 40 through a belt (not illustrated) and the like in a direct contact manner, and by operating the compressor.
Therefore, since a part of power of the crank shaft 40 is used for the compressor, when the air conditioner 50 is operated when the vehicle is driven, additional fuel is consumed in order to maintain the same output, and thereby, there are problems in that fuel efficiency deteriorated like the related art, and output is decreased when the same amount of fuel is consumed.
In addition, the vehicle including the engine 10 is tuned in order to meet emission gas regulation and fuel efficiency target values when the vehicle is developed, but additional tuning and building of control logic need to be performed to prepare for a situation when the air conditioner 50 is operated, and thus considerable cost is required, and due to technical difficulty in applying mass production of a tuning technology, emission gas frequently exceeds an allowable value defined by the regulation when the air conditioner 50 is operated.
In addition, as illustrated in FIG. 4, in the related art, auxiliary machinery 60 such as a coolant pump 61, a fuel pump 62, and a fuel fan (or a cooling fan) 63, which assists driving of the engine 10, is also connected to the crank shaft 40 and operated, and thus, as described above, there are problems in that additional fuel is consumed in order to maintain output of the crank shaft 40 when the auxiliary machinery 60 is operated, and thereby, fuel efficiency deteriorates.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.